Separation of components from a reaction product mixture of water isobutyric acid and methacrylic acid by phase separation and distillations

ABSTRACT

To separate aqueous and organic components of a mixture of isobutyric acid, water and methacrylic acid, the mixture is initially separated by salting out by means of a water soluble electrolyte e.g. sodium sulfate, which causes separation of aqueous and organic phases. Residuals in each phase are distilled off as a low-boiling mixed distillate resembling an azeotropic mixture which is returned for repeated separation by salting-out. Organics are further separated by fractional distillation.

United States Patent Witheford 51 May 16, 1972 [54] SEPARATION OFCOMPONENTS FROM A REACTION PRODUCT MIXTURE OF WATER ISOBUTYRIC ACID ANDMETHACRYLIC ACID BY PHASE SEPARATION AND DISTILLATIONS [72] Inventor:John Maurice Witheford, Wyckoff, NJ.

[73] Assignee: American Cyanamid Company, Stamford,

Conn

[7.7] Filed MBLJI, 1970 [21] Appl.No.: 24,362

AOUEOUS SOLUTION OF ISOBiqUTYR/C N0 METHACRYL /C 46/05 2,266,004 12/ l941 Coes ..203/15 2,111,510 3/1938 Loder. ....260/526 3,370,087 2/1968Hargis ....260/526 3,337,740 8/1967 Gray et a1. ....260/526 2,379,6257/1945 Coes ....260/526 2,922,815 1/1960 Faerber .260/526 2,551,6255/1951 Morrell et a] ..203/53 Primary Examiner-Wilbur A. Bascomb, Jr.AttorneyGordon L. Hart [57] ABSTRACT To separate aqueous and organiccomponents of a mixture of isobutyric acid, water and methacrylic acid,the mixture is initially separated by salting out by means of a watersoluble electrolyte e.g. sodium sulfate, which causes separation ofaqueous and organic phases. Residuals in each phase are distilled off asa low-boiling mixed distillate resembling an azeotropic mixture which isreturned for repeated separation by salting-out. Organics are furtherseparated by fractional distillation.

6 Claims, 1 Drawing Figure .400 9.4 M1 30 SALTING-0UT H 0 AGEIVT 2 4TWO-PHASE SEPARA T/ON RECYCLE LIGHT ORGAN/C PHASE HEAVY AQUEOUS PHASED/ST/LL OFF ORGAN/CS WITH SOME WATER FOR RECYCL E DIST/LL OFF WATER WITHSOME ORGAN/CS FOR RECYCLE ESSENTIALL ORGAN/CS ESSENTIALL) WATER ANDELECTROLYTE Patented May 16, 1972 AQUEOUS SOL U T/O/V OF ISOBU T YR/O AND METHACRYL IO ACIDS ADD SAL T/NGY-OUT AGE/VT TWO-PHASE .SEPA/PA T/O/V--L/GH T ORGAN/C PHASE :12: :HEAVY AQUEOUS PHASE- ag. N02 S04 H2504 0/577!. L OFF ORGA lV/CS WITH SOME WATER FOR RECYCLE O/ST ILL OFF WA TER W/TH SOME ORGAN/CS FOR REOYOLE ESSENTIALL Y ORGAN/CS ESSENTIALL Y WATERAND ELECTROLYTE INVENTOR. JOHN MAURICE W/Tl-IEFORD A 7' TOR/V5 YSEPARATION OF COMPONENTS FROM A REACTION PRODUCT MIXTURE OF WATERISOBUTYRIC ACID AND METHACRYLIC ACID BY PHASE SEPARATION ANDDISTILLATIONS The invention relates to separation of aqueous and organiccomponents from a mixture comprising isobutyric acid, methacrylic acidand water.

Copending U.S. Pat. application Ser. No. 818,818, filed Apr. 23, 1969 byKin I-Isueh-Yuan Tsu titled Catalytic Process for Manufacture ofUnsaturated Acids and Esters describes a process comprising catalyticdehydrogenation of isobutyric acid (IBA) to make methacrylic acid (MAA).The product mixture obtained from the product condensation step in apreferred embodiment of that process comprises a mixture of isobutyricacid, methacrylic acid and water. Ordinarily these three components forma mutual solution from which water and the organic components cannot becompletely separated by simple fractional distillation because of thepresence of the two binary azeotropes of water with MAA (23 percent MAA,B. P. 99 C. at atm. press) and water with IBA (28 percent IBA, B. P. 98C. at atm. press). Upon atmospheric distillation of the aqueous mixedacid composition the lowest boiling fraction is distilled over at about99 C. In this first fraction the sum of the IBA and MAA concentrationsis in the range of about 20-30 percent by wt. and a low-boilingdistillate of about the same water to organics ratio continues todistill at the same temperature until either all of the water or all ofthe organic acids have been removed by distillation.

An object of the invention is to provide an efficient method forseparation of the aqueous and organic components of a mixture comprisingwater, isobutyric acid and methacrylic acid.

According to the invention an electrolyte such as sodium sulfate orsulfuric acid is added to an aqueous solution of isobutyric acid andmethacrylic acid in amount sufficient to cause saltingout, which isseparation of the mixture into two immiscible phases; one phase is anaqueous sodium sulfate solution and other phase is an organic solutionof the two acids. These two immiscible phases of the mixture arephysically separated as by gravity in a decanter to obtain a principallyaqueous solution of electrolyte with only very minor proportions of theorganic components and a principally organic solution with only a veryminor proportion of water. Each of these separated solutions is thendistilled to remove only the low boiling distillate described above.From the organic phase, the small proportion of water is entirelyremoved in the low-boiling distillate and, similarly, from the aqueoussodium sulfate solution the residual organics are removed in thelow-boiling distillate. The small proportion of low-boiling distillatefrom each phase is collected and separated by repeating the same stepsjust described.

After distillation of the low-boiling mixture from the organic solution,the anhydrous mixture of IBA and MAA may be further separated andpurified by fractional distillation. Because of the very close boilingpoints of isobutyric acid and methacrylic acid, their separation byfractional distillation requires a fractionating column with about 40 to50 plates or the equivalent, even with high reflux ratio in the rangeabout 8-10. To prevent polymerization of methacrylic acid duringdistillation it is preferred to operate at low distillation temperaturesand for this reason, vacuum distillation is preferred. When theinvention is employed in connection with the dehydrogenation process asmentioned above, isobutyric acid recovered by the present process may bereturned to the dehydrogenation process feed stream. The methacrylicacid residue of the vacuum distillation constitutes the purified productof the dehydrogenation process.

To achieve an efficient salting-out effect with sodium sulfate it ispreferable to use enough sodium sulfate to provide, with the water ofthe mixture, at least 0.2 normal aqueous sodium sulfate solution andpreferably 1 to 4 normal solution. Higher sodium sulfate concentrationsmay be used up to saturation. lf another electrolyte is used, theconcentration similarly should be high enough to salt out most of theorganic components. Sodium sulfate may be present in the water that isused initially to make the mixture; for example, after thedehydrogenation process the water used for condensation may bepreviously prepared aqueous sodium sulfate solution. In such anembodiment, initial formation of the homogeneous ternary solution isinhibited and the aqueous and organic components of the mixture remainfor the most part in separate phases. In other embodiments sodiumsulfate may be added directly to an already solubilized mutual solutionof the three components to cause the salting-out effect with separationof the components into aqueous and organic phases.

DESCRIPTION OF THE DRAWING The accompanying schematic drawingillustrates diagrammatically for the sake of illustration the operationand the system for carrying out the process of this invention.

Following is an example setting forth in detail a most preferred mode ofcarrying out the invention as illustrated schematically in the drawing.

EXAMPLE 1 Vapors consisting essentially of water, isobutyric acid andmethacrylic acid mixed with light gases from the catalyticdehydrogenation process described in U. S. Pat. application Ser. No.818,818, mentioned above, are condensed in an aqueous spray chamberusing about 2 normal sodium sulfate aqueous solution for the aqueousspray. Non-condensables, i.e. light gases pass upward through ascrubbing column counter-current to a stream of aqueous solution ofsodium sulfate and are vented. Liquids from this column consist ofaqueous sodium sulfate solution mixed with condensed methacrylic acidand isobutyric acid. The mixture is further cooled and led to adecanter. Proportions by weight of the components in the liquid mixturetaken from the condenser are approximately 5-15 parts by wt. isobutyricacid, 10-20 parts by wt. methacrylic acid and 65-85 parts sodium sulfateaqueous solution. Neither isobutyric acid nor methacrylic acid is verysoluble in the aqueous sodium sulfate solution and in the decanter themixture separates into an aqueous layer and an organic layer. Theaqueous layer contains 3-5 percent by wt. organics and the organic layercontains 5-10 percent by wt. water. The organic layer is drawn from thedecanter and fed to a vacuum distillation column operated to distillover the lowest boiling distillate which is about percent water and 20percent mixed organic acids. Residue from the distillation consistsessentially of an anhydrous solution of isobutyric and methacrylicacids. The distilled solution recovered overhead is returned to thedecanter where sodium sulfate may be added. In a continuous process thereturned solution picks up sodium sulfate in the decanter from theincoming condenser liquids and separates into immiscible phases asbefore. These phases are separated and distilled as before.

The anhydrous organic acid residue is led to a second vacuumdistillation column having 50 plates, operated at a reflux ratio of 10where isobutyric acid is distilled overhead and essentially puremethacrylic acid product is recovered as distillation bottoms.

The aqueous sodium sulfate solution from the decanter is led to anotherdistillation column which is operated at atmospheric pressure. In thisdistillation the small proportions of isobutyric and methacrylic acidremaining in the aqueous solution are distilled overhead in the same 80percent water, minimum boiling distillate described above, and this iscondensed and returned to the decanter for further separation, the sameas the distillate from the organic solution. Aqueous residue isessentially free of isobutyric and methacrylic acids and this sodiumsulfate aqueous solution can be returned to the spray chamber for reusein the dehydrogenation product condensation step. In some cases it maybe preferred to concentrate the sodium sulfate solution in an evaporatorbefore the solution is recycled.

The invention has been described with reference to specific embodiments,however, modifications and variations may be made within the scope ofthe invention. For example, another suitable electrolyte may besubstituted for sodium sulfate. Any electrolyte that does not react withor dissolve in the organic phase may be used. Sulfuric acid, forexample, is a suitable electrolyte for the purpose. Other mixturescomprising the same three components but varying in relativeconcentrations of any of the components of the mixture may be separatedby a process comprising the invention. Separation of the ternary mixtureas described may find other applications apart from the dehydrogenationprocess and its product condensation which are described in the specificexample above.

I claim:

1. A method for separating the aqueous and organic components of amixture of water, isobutyric acid and methacrylic acid comprising thesteps of:

a. dissolving in the water component of said mixture an electrolyte inamount sufficient to salt out the mixture to form immiscible organic andaqueous phases,

b. separating the immiscible phases so formed as separate aqueous andorganic solutions and distilling from each of the separated organic andaqueous solutions a low-boiling distillate which consists essentially ofwater, isobutyric acid and methacrylic acid leaving separate organic andaqueous residues respectively consisting essentially of a mixture ofisobutyric acid and methacrylic acid and an aqueous solution of saidelectrolyte.

2. A method defined by claim I wherein said electrolyte is sodiumsulfate.

3. A method defined by claim I further comprising the steps of repeatingthe defined steps (a) and (b) on the distillate mixtures obtained fromthe first defined step (b).

4. A method comprising the steps of:

a. mixing condensate comprising isobutyric acid and methacrylic acidwith water which contains dissolved electrolyte in quantity sufficientto salt out the mixture thereby forming immiscible organic and aqueousphases,

b. separating the immiscible phases so formed as separate aqueous andorganic solutions and distilling from each of the separated organic andaqueous solutions a low-boiling distillate which consists essentially ofwater, isobutyric acid and methacrylic acid leaving separate organic andaqueous residues respectively consisting essentially of a mixture ofisobutyric acid and methacrylic acid and an aqueous solution of saidelectrolyte.

5. A method defined by claim 4 wherein said electrolyte is sodiumsulfate.

6. A method defined by claim 4 further comprising the steps of repeatingthe defined steps (a) and (b) on the distillate mixtures obtained fromthe first defined step (b).

2. A method defined by claim 1 wherein said electrolyte is sodiumsulfate.
 3. A method defined by claim 1 further comprising the steps ofrepeating the defined steps (a) and (b) on the distillate mixturesobtained from the first defined step (b).
 4. A method comprising thesteps of: a. mixing condensate comprising isobutyric acid andmethacrylic acid with water which contains dissolved electrolyte inquantity sufficient to salt out the mixture thereby forming immiscibleorganic and aqueous phases, b. separating the immiscible phases soformed as separate aqueous and organic solutions and distilling fromeach of the separated organic and aqueous solutions a low-boilingdistillate which consists essentially of water, isobutyric acid andmethacrylic acid leaving separate organic and aqueous residuesrespectively consisting essentially of a mixture of isobutyric acid andmethacrylic acid and an aqueous solution of said electrolyte.
 5. Amethod defined by claim 4 wherein said electrolyte is sodium sulfate. 6.A method defined by claim 4 further comprising the steps of repeatingthe defined steps (a) and (b) on the distillate mixtures obtained fromthe first defined step (b).